Leakage Accidents Research Articles

Experimental investigation on flame characteristics in a linear array of dual spill fire

In the process of petroleum production and transportation, a porous leakage accident can easily lead to combustion behaviors such as fire merging, resulting in more severe consequences. This study explores the combustion characteristics of merging spill fires through experimental investigations, incorporating dual leakage holes with varying spacing to examine their impact on the combustion process. The experimental results suggest that the flame height undergoes a pattern of initial decrease followed by an increase with the gradual expansion of leakage spacing, owing to the coupling effects of air entrainment and thermal radiation feedback within the additional entrainment zone. Based on the developmental pattern of flames with respect to leakage spacing, this study categorizes the dual spill fire into three states: which are: (1) full merging state, (2) intermittent merging state, and (3) separation state. The flame height prediction model is established for different merging states, considering parameters such as the fuel discharge rate and the leakage spacing of dual spill fire. The experiment reveals that the flame pulsation frequency (FPF) of the spill fire follows the pattern observed in pool fire FPF, and an FPF model for dual spill fire in all states is obtained through the fitting. Finally, the coupled heat transfer between dual fire sources is considered, and a burning rate model for dual spill fire in intermittent merging states is established.

Research on active and passive schemes for safety improvement of nuclear energy hydrogen production system

Nuclear hydrogen production has the advantages of large-scale and low carbon emissions, and is expected to play an active role in the energy transition process. However, the storage and transportation of hydrogen pose potential risks of leakage and diffusion when connected to high-pressure hydrogen storage tanks and pipelines. To address this concern, this study focused on designing three distinct safety improvement schemes tailored for potential hydrogen leakage accidents. These schemes encompassed a passively distributed arrangement of obstacles (Scheme 1), a passively centralized arrangement of obstacles (Scheme 2), and an active fan array blowing (Scheme 3). Numerical simulation methods were applied on extensive spatial scales for relevant calculations. The results revealed that all three schemes effectively reduced the diffusion distance of combustible hydrogen. Specifically, at lower ambient wind speeds, Scheme 1, Scheme 2, and Scheme 3 achieved the shortest diffusion distances of 123 m, 56 m, and 46 m, respectively. Meanwhile, at higher ambient wind speeds, the corresponding distances were 282 m, 100 m, and 79 m. These results collectively offer valuable insights to mitigate the risk of leakage accidents in nuclear hydrogen production systems.

Development of an AI-based image/ultrasonic convergence camera system for accurate gas leak detection in petrochemical plants

Outdoor pipeline leaks are difficult to accurately measure using existing concentration measurement systems installed in petrochemical plants owing to external air currents. Besides, leak detection is only possible for a specific gas. The purpose of this study was to develop an image/ultrasonic convergence camera system that incorporates artificial intelligence (AI) to improve pipe leak detection and establish a real-time monitoring system. Our system includes an advanced ultrasonic camera coupled with a deep learning-based object-detection algorithm trained on pipe image data from petrochemical plants. The collected data improved the accuracy of detected gas leak localization through deep learning. Our detection model achieves an mAP50 (Mean average precision calculated at an intersection over union (IoU) threshold of 0.50)score of 0.45 on our data and is able to detect the majority of leak points within a system. The petrochemical plant environment was simulated by visiting petrochemical plants and reviewing drawings, and an outdoor experimental demonstration site was established. Scenarios such as flange connection failure were set under medium-/low-pressure conditions, and the developed product was experimented under gas leak conditions that simulated leakage accidents. These experiments enabled the removal of potentially confounding surrounding noise sources, which led to the false detection of actual gas leaks using the AI piping detection technique.

An integrated risk assessment method for urban areas due to chemical leakage accidents

Chemical parks which hold large inventories of hazardous materials have become one important type of urban critical infrastructure. The hazardous chemical leakage such as toxic gas leakage has emerged in recent years, resulting in not only serious environmental pollution but also catastrophic consequences to certain urban areas. It is critical to make scientific risk assessment for such events to reduce negative effects. To address this issue, an integrated urban risk assessment (IURA) method coupling consequences of chemical leakage accidents and the vulnerability of local population is proposed in this work. The threat zones and hazard maps of toxic gas dispersion are present by using the ALOHA software. The population vulnerability is decided by three indicators including exposure, sensitivity, and adaptive capacity of residents in affected areas, the Grey Correlation-TOPSIS (GC-TOPSIS) method is used to rank the vulnerability of different regions. The ArcGIS software is applied to generate an integrated risk map through superimposing the hazard map and the population vulnerability map. The original risk matrix evaluation results were subdivided using the Borda count method. A case about an industrial city in Hubei, China is analyzed to test the method. Result shows the new integrated risk assessment method is more accurate and effective, which is beneficial for the government to develop emergency plans and enhance the safety of people.

Causative factors and risk prediction model of hydrogen leakage accidents: Machine learning based on case evidence

This study innovatively derives a risk prediction model for hydrogen leakage accidents based on existing case evidence by combining MORT (Management Oversight and Risk Tree) with machine learning algorithms. 30 hydrogen leakage accidents causative factors are derived by analyzing 23 accident cases through MORT, and constructed a dataset of hydrogen leakage accident causative factors through data quantification. Using feature selection to optimize the risk indicators, 14 salient feature indicators are selected from the 30 full feature indicators. Two cross-validation strategies are introduced and combined with six machine learning models to establish 24 working conditions for numerical comparison experiments. The results show that the support vector machine model based on stratified K-fold cross-validation strategy has the best prediction performance, with the model Accuracy of 0.939, Precision of 0.848, Recall of 0.848, F1-score of 0.848, and AUC score of 0.98. This will effectively solve the problem of hydrogen leakage risk prediction and accident prevention in industrial systems.

Numerical simulation of leakage, dispersion and explosion behavior of LPG in kitchen

ABSTRACT The frequent occurrence of kitchen gas explosion accidents has raised widespread attention to gas safety. This article takes kitchen as the research object, and explores the dispersion law of LPG leakage in kitchens and the influence of ignition at different leakage time on explosion consequences by establishing LPG leakage and explosion models. The results show that the process of LPG leakage in a closed kitchen can be divided into three stages: initial kinetic energy dominant stage, gravity expansion stage, and passive dispersion stage. Propane forms a non-uniform concentration field in the kitchen that gradually decreases from bottom to top, filling the entire kitchen in 583 s. When an explosion occurred in the kitchen center, the initial burst of flame spreads around in a fireball. After 115 ms and 122 ms, the explosion overpressure causes the door and window to be destroyed respectively, and the flames stretch toward the door and window. The flames are then concentrated mainly in the lower area where the fuel is more adequate. In the later stage of the deflagration reaction, the flame propagates toward the upper area of the kitchen under buoyancy. The explosion consequences of LPG non-uniform gas clouds show a pattern of first intensifying and then weakening with the leakage time. The explosion consequences are most severe when ignited about 300 s after the leakage. The maximum explosion overpressures at the center of the kitchen, door, and window were 67.15 kPa, 28.12 kPa, and 27.92 kPa, respectively. The research results can provide reference for emergency response, consequence assessment, and kitchen safety design for kitchen LPG leakage and explosion accidents..

Research progress and development trends of hydrogen explosion suppression materials and mechanisms

In order to effectively control and reduce the destructive effects caused by hydrogen leakage and explosion accidents, continuously improving the theoretical system of hydrogen suppression. Based on a survey of literature, this article reviews and discusses the current research status of hydrogen explosion characteristics, explosion suppression materials, and explosion suppression mechanisms. In terms of research on hydrogen explosion characteristics, the impact of initial conditions on macroscopic parameters such as explosion limit, explosion pressure and flame propagation speed were mainly studied. In terms of research on hydrogen suppression, summarizes the research progress of hydrogen explosion suppression materials in recent years from five aspects: inert gas, water mist, solid powder, halogenated hydrocarbons and composite suppression. The suppression effects and suppression mechanisms of different materials were comparatively analyzed. The analysis found that the explosion suppression mechanism of inert gas is mainly physical inerting, and a higher concentration of inert gas is required to completely suppress hydrogen explosion. The explosion suppression mechanism of fine water mist is mainly evaporation and heat absorption, but it cannot completely suppress lean fuel hydrogen explosion. Solid powder materials have almost no inhibitory effect on hydrogen explosion. The explosion suppression mechanism of halogenated hydrocarbons is mainly to eliminate H radicals, but halogenated hydrocarbons have an promoting effect on lean fuel hydrogen. The suppression effect of composite explosion suppressants is better than that of a single explosion suppressor. However, there are currently few studies on the suppression of hydrogen explosions by composite suppressants, and the mechanism of explosion needs to be improved. The article proposes that hydrogen absorption materials, eliminate H radical targeted suppression materials and composite explosion suppression materials are the focus of research on hydrogen suppression materials. Using advanced optical diagnostic technology to study the concentration of radicals and explosion flow field characteristics, and using kinetic simulation software to reveal the complex chain reaction process are important means to study the mechanism of hydrogen explosion suppression. Large-scale explosion suppression experiments are more instructive for engineering applications, but there is a lack of large-scale equipment and experimental research.

Research on Multi-Point Monitoring Data Grid Model and Inversion Positioning Method for Gas Leakage in Oil and Gas Stations

The safe and stable operation of oil and gas stations makes a positive contribution to the stability and reliability of the natural gas supply. In order to reduce the impact of leakage and diffusion accidents in the station, it is necessary to develop an effective method to monitor and locate the leakage source quickly and accurately. This study proposes a multi-point monitoring data grid model to achieve the full-coverage monitoring of oil and gas stations. In addition, on this basis, a leakage source inversion positioning model is established to realize the leakage positioning of the station. A field experiment was carried out with an oil and gas station as an example. The results show that the optimal layout of points needs to consider the influence of environmental factors, confirmed by computational fluid dynamics (CFD) simulation. The optimized data interpolation not only reduces the cost of the monitoring point layout. In addition, through the comparison of multi-objective optimization algorithms and a robustness test, it can be found that the convergence efficiency and accuracy of the inversion positioning algorithm in this study have been greatly improved. Compared with the manual auxiliary positioning method, this method effectively solves the problem of leakage monitoring and positioning of oil and gas stations, and can achieve the purpose of leakage risk monitoring and “reducing cost and increasing efficiency”.

Experimental study on leakage characteristics of gas-liquid two-phase flow in a horizontal pipe

Oil and gas pipeline leakage accidents caused by aging and third-party damage have increased, resulting in polluting the ecological environment and jeopardizing life and property safety. A detailed and systematic investigation on the leak characteristics of oil and gas two-phase pipelines is significantly urgent. The leak experiments were performed on a horizontal tube with a diameter of 32 mm. There was a 3 mm round leakage hole at the bottom of the tube. The distance of the leakage hole from the pipe inlet was 4.8 m. Three inlet flow patterns, including stratified flow, slug flow, and annular flow via adjusting the gas superficial velocity (1.73 m/s ≤ USG ≤ 24.19 m/s) and liquid superficial velocity (0.017 m/s ≤ USL ≤ 0.415 m/s), were obtained. The conclusions point out that the type of leakage, whether it is mainly liquid or both gas and liquid, depends on the USG. The degree of phase separation in stratified flow is the greatest among the three inlet flow patterns, with a maximal phase separation efficiency (η) of 0.403. Slug flow has the least phase separation degree. Interestingly, the η is directly proportional to the inlet mass fraction only for slug flow. The harmonic frequency that appeared in the power spectral density curves for the pressure difference of leakage hole in slug flow, indicates that leakage is not a standard periodic event. The liquid velocity loss is primarily related to the gas leakage mechanism. These findings can provide new insights into two-phase pipeline leak detection and accident consequence prediction.

RETRACTED ARTICLE: Preliminary risk assessment of in-vessel leakage accident in ITER

The ITER project is one of the largest international cooperative scientific projects in the world, aiming to verify the feasibility of magnetic confinement controlled nuclear fusion technology and provide a technical basis for the subsequent construction of fusion energy power stations. The success or failure of ITER will greatly affect the commercialization process of fusion energy. The probabilistic safety assessment (PSA) was a powerful means to evaluate the risk and reliability of nuclear facility and achieved great success in safety assessment of fission power plants. Based on this, the PSA progress for ITER was proposed in this paper. And the in-vessel leakage accident was investigated to verify the effectiveness of proposed method. The result shows the maximum possible radiological consequences of ITER in-vessel leakage accident of ITER is 1.6E−3 mSv, and the frequencies of this consequence is 1.63E−8/year. The reason of this consequence was also discussed in this paper. Those result could provide some valuable reference for radiation risk assessment and safety supervision of fusion commercial reactor in the nuclear future.

Leakage detection based on variational mode decomposition and long short-term memory neural network

In the process of long-term continuous operation, fluid transportation pipelines are prone to leakage accidents. Therefore, this study investigates the detection of small-sized leaks with a leakage aperture of 13 mm in pipes with a diameter of 100 mm. The experimental investigation is conducted under the following operating conditions: volume flow of 25-80 m3/h, pressure of 100-200 kPa. The variations in volume flow and pressure signals during leak occurrences are analysed. To mitigate the interference caused by noise, the variational mode decomposition (VMD) method is introduced. The VMD effectively reduces noise interference in the signals. Furthermore, the denoised signals are utilized to establish a long short-term memory neural network (LSTM). The LSTM model achieves a high accuracy rate of 91.67% for the entire dataset.

Facile preparation of poly(melamine formaldehyde) sponge/bacterial nanocellulose composite for oil-water separation

The treatment of a large amount of oil-water mixture generated by oil leakage accidents is an environmental issue that cannot be ignored. Achieving fast and efficient oil-water separation is a goal pursued by both academia and industry. In this paper, poly(melamine formaldehyde) (PMF) sponges were modified by the hydrophilic bacterial nanocellulose (BNC) through mild and facile conditions. With increasing the concentration of BNC dispersion used, the pore size of the composite decreases. The water contact angle of the obtained PMF/BNC composite surface is 0° or so, and the underwater oil contact angle is greater than 150°. Based on its hierarchical pore structure, hydrophilicity and oil repellency, the PMF/BNC composite exhibits excellent oil-water separation efficiency and water treatment flux for layered oil-water mixture (>1.0×107L/(m2·h·bar)). In addition, the PMF/BNC composite also exhibits high water treatment flux and oil-water separation efficiency (> 95%) for oil-water emulsion with and without surfactant. Stacking several composite slices could achieve higher oil-water separation efficiency.

Hydrogen and temperature measurement using a functionalized superstructure of Bragg gratings in a helical-core fiber

As decarbonization is urgent in global climate, hydrogen, of which the product is pure water after burning, becomes a potentially clean and sustainable energy source as a replacement for fossil fuels. However, the hydrogen storge is challenging due to the highly flammable and explosive properties, limiting its enormous applications in industries. Real-time and sensitive detection of hydrogen is thus imperative to avoid leakage accidents, while the sensors based on electric signals have the risk of spark or arc discharge which may induce explosion. Here, we propose and experimentally demonstrate an optical hydrogen sensor using a functionalized superstructure of Bragg gratings in a helical-core fiber with a thin palladium film. Due to the cross sensing of the two sets of gratings, simultaneous detection of hydrogen concentration and temperature can be realized. By modifying the device diameter using wet etching technique, the sensitivity of hydrogen concentration is enhanced by 2.7 times. The utilization of the superstructure of Bragg gratings sampled in the helical-core fiber provides a promising platform for reliable and safe sensing of hydrogen with the ability of simultaneous monitoring of temperature.

Field experimental study of high expansion foam coverage after LNG leakage

With the rapid development of the world’s natural gas industry, LNG (Liquefied Natural Gas) has received widespread attention as a clean energy source. However, the leakage accidents of LNG are usually accompanied by safety hazards such as explosions, low temperatures, and phase transitions. In this study, the field experiment is carried out to cover LNG leakage pool with HEF (High-Expansion Foam). In the process of LNG leakage, when the ambient temperature at the bottom of the reservoir drops to about − 82.3 °C (the critical temperature of LNG), the ambient temperature would rise briefly due to the effect of phase transition. Meanwhile, the temperature distribution of different vertical and horizontal positions in the reservoir during the process of leakage is analyzed. Besides, it is also found that the density of the spilled vapor is much lower than that of the air, but the water in the surrounding air encounters the cryogenic vapor to condense into small droplets, the small droplets entrap part of the flammable gas during the process of settling to the ground, therefore, the flammable vapor still shows a heavy gas effect. During the initial period of HEF coverage, evaporation from the liquid pools accelerates, resulting in a 386% increase in peak concentration of methane above the reservoir. Nevertheless, when HEF application is maintained an effective thickness, it can effectively reduce the methane vapor concentration downstream of the reservoir near the surface to less than 1/2 LFL (1/2 of the Lower Flammability Limit). In general, the large-scale field experiments have far-reaching engineering significance and reference value for the occurrence and emergency treatment of LNG leakage accidents under actual working conditions.

Investigation of urban natural gas pipeline leak and resulting dispersion in a semi-closed space: A case of accident in Shiyan, China

Pipeline is the most common way for delivering natural gas to the urban areas. Nevertheless, pipeline leak accidents can pose significant threats to human life and property safety. This paper investigates the characteristics of urban natural gas pipeline leaks and the resulting gas dispersion in a semi-closed space using a 3D Computational Fluid Dynamics (CFD) model. The characteristics of a pipeline leak is examined considering the impact of shape, dimensions, and location of the aperture. The migration of natural gas in a semi-closed space is tracked, considering the impact of leak location and orientation. To illustrate the model, a real-life case study is conducted to simulate flammable gas release and dispersion resulting from an urban natural gas pipeline leak. The outcome can guide the monitoring and mitigating the consequences of urban natural gas pipeline leaks.

Highly efficient molecular film for inhibiting volatilization of hazardous nitric acid

Nitric acid, an important basic chemical raw material, plays an important role in promoting the development of national economy. However, such liquid hazardous chemicals are easy to cause accidental leakage during production, transportation, storage and use. The high concentration and corrosive toxic gas generated from decomposition shows tremendous harm to the surrounding environment and human life safety. Therefore, how to inhibit the volatilization of nitric acid and effectively control and block the generation of the toxic gas in the first time are the key to deal with the nitric acid leakage accident. Herein, a new method of molecular film obstruction is proposed to inhibit the nitric acid volatilization. The molecular film inhibitor spontaneously spread and form an insoluble molecular film on the gas-liquid interface, changing the state of nitric acid liquid surface and inhibiting the volatilization on the molecular scale. The inhibition rate up to 96% can be achieved below 45 °C within 400 min. Cluster structure simulation and energy barrier calculation is performed to elucidate the inhibition mechanism. Theoretical analysis of energy barrier shows that the specific resistance of the inhibitor significantly increased to 460 s·cm−1 at 45 °C, and the generated energy barrier is about 17,000 kJ·mol−1, which is much higher than the maximum energy required for nitric acid volatilization of 107.97 kJ·mol−1. The molecular film obstruction strategy can effectively inhibit the volatilization of nitric acid. This strategy paves the way for preventing the volatilization of liquid hazardous chemicals in accidental leakage treatment.

Consequences of subsea CO2 blowouts in shallow water

Safety and risk assessment of the offshore geological storage of carbon dioxide (CO2) in the Carbon Capture, Utilization, and Storage (CCUS) value chain needs the evaluation of the consequences of possible accidental submarine CO2 leakages, including releases having high flow rate and very long duration, as blowouts. An innovative procedure for the estimation of the effects of submarine blowouts in shallow water was developed, based on the integration of specific sub-models. A model for blowout simulation is used to predict the features of the source term. The fate of the submarine plume is then assessed. Finally, the atmospheric dispersion of the surfacing gas is simulated, to estimate damage distances. The application of the methodology to a set of case studies evidences that in extremely shallow water the threshold distances of the gas cloud dispersing in the air can be higher for CO2 than for natural gas. However, when considering higher water depths, the release of CO2 to the atmosphere is strongly attenuated by the dissolution of CO2 in the water column.

Experiment and modeling of stochastic ignition and combustion of fuel droplets impacting a hot surface

The ignition dynamic of liquid fuel droplets impacting hot surfaces is critical for fire-safety analysis in engineering systems, as well as for controlling wall-filming effects in IC engines. The scenario of slow fuel-leakage rates poses challenges associated with the stochastic processes of droplet splashing, break-up, turbulent mixing, and combustion. To address this, we conduct controlled experiments of liquid n-heptane droplets impacting a heated surface in the Leidenfrost regime, targeting the individual-droplet-deposition conditions. The experiment encompasses a range of surface temperatures and droplet-deposition rates. The experiments are complemented by theoretical analysis, where we developed a stochastic low-order numerical model, demonstrating good accuracy for predicting ignition probability and overall combustion dynamics. Notably, we observe a broad region of intermittent combustion behavior, with ignition probability varying based on surface temperature and droplet deposition rate. Additionally, we find that the transition to consistent ignition relies heavily on both surface temperature and deposition rate. Experimental and numerical model results shed light on the roles of the complex interplay between droplet breakup, chemical kinetics, and evaporation and mixing time scales, as well as the interaction among subsequent droplet combustion events, in governing the ignition and combustion of impacting droplet trains. The revealed dynamic of droplet/hot-surface ignition and the proposed stochastic model hold promise for advancing predictive capabilities of hot-surface-induced ignition and combustion arising from accidental leaks in flammable-liquid piping and wall-filming, particularly in the stochasticity-dominated individual-droplet-deposition regime.

Optimization of Emergency Resource Dispatch for Overseas Long-distance Natural Gas Pipeline Leaks

Overseas long-distance natural gas pipelines usually span across multiple regions or even countries, facing more severe environmental conditions and more prone to leakage and other accidents, and the study of the optimization method of emergency resource scheduling for overseas long-distance natural gas pipeline leakage accidents can help to reduce the casualties and property losses. Therefore, this paper establishes an emergency resource scheduling model in line with the emergency disposal mechanism of overseas long-distance natural gas pipeline leakage accidents, takes into account the variability of the operating ability of maintenance personnel, and improves the accuracy of the scheduling program to a certain extent, and also considers the actual environment of overseas long-distance natural gas pipelines, takes into account the impact of landslides on the emergency scheduling time, and calculates the probability of landslides occurring in the landslide point by using the interpolated value of rainfall The rainfall interpolation is used to calculate the probability of landslide at the landslide point, and the emergency dispatching time is corrected to make the dispatching program more in line with the actual demand. The analysis of the results shows that the emergency resource scheduling time is dominant in the case of small amount of maintenance and repair work and short total maintenance and repair time.

Numerical Simulation of Crude Oil Leakage from Damaged Submarine-Buried Pipeline

Oil spill accidents in damaged submarine-buried pipelines cause tremendous economic losses and serious environmental pollution. The accurate prediction of oil spills from subsea pipelines is important for emergency response. In this study, the volume-of-fluid model, realizable k–ε turbulence model, and porous-medium model were employed to describe the process of an oil spill from a submarine pipeline to the sea surface. The effects of seawater density, seawater velocity, and pipeline buried depth on the transverse diffusion distance of crude oil and the time at which crude oil reaches the sea surface were obtained through numerical calculations. The calculation results show that, with a decrease in seawater density and an increase in seawater velocity and pipeline depth, the diffusion rate of crude oil decreases significantly, the maximum transverse diffusion distance increases and crude oil takes a long time to reach the sea surface. In particular, compared with a sea density of 1045 kg/m3, the transverse distance of a sea density of 1025 kg/m3 is increased by 0.091 m. When the seawater velocity is greater than 1.5 m/s, the diffusion of crude oil in seawater is significantly affected, the seawater velocity increases to 0.35 m/s, and the transverse diffusion distance of oil to the sea surface increases to 12.693 m. When the buried depth of the pipeline reaches 0.7 and 1.3 m compared to 0.1 m, the diffusion widths of crude oil in sea mud rise by 20% and 32.5%, respectively. The time required for crude oil to reach the sea surface and the transverse diffusion distance of crude oil migrating to the sea surface were analyzed using multiple regression, and the fitting formulas were obtained. The results provide theoretical support for accurately predicting the leakage range of submarine-buried pipelines and provide valuable guidance for submarine-buried pipeline leakage accident treatment schemes.